Movable high security or vault doors are devices which periodically open and periodically close and lock openings.
Conventional locking systems have certain weaknesses which fail to satisfy the usual modern safety and security requirements for door locks. Known attempts to avoid weaknesses in conventional systems involve the security aspects. The steps taken are many and varied, and mainly relate to the armoring.
In spite of such protective measures, the position of the locking points must remain secret. If it is known, a persistently performed destruction of the protective means would result in unauthorized opening of the door. The position of the locking points, which normally should be unknown, can be found out so that the position of the lock is known. Within certain limits the position of the lock is determined by the lock-opening device on the outside of the armored door. This narrowing down of the possible area where the locking points may be situated, together with knowledge of the type of lock (individual types of lock are extremely widespread) may permit opening of the safety door, even without a key or code. Moreover, the number of locks, and therefore, the number of locking points is very limited, since every lock requires a connecting element which extends outside directly through a hole in the armor, and an operating element on the outside which indicates the position of the lock and locking point.
Another serious weakness is inherent in the lock mechanism itself. The combination locks used in safety closures can be unlocked by a code, defined inside the lock by the relative positioning of a predetermined combination of a number of coding discs. The "inner" unbolting enables the lock mechanism to be actuated. The "outer" unbolting, for example, between the door and the frame enables the safety closure to open.
In a correctly locked safety security door (for example, an armored door), the combination lock is actuated by decoding the coding discs. At any angular position of the discs in relation to one another, a deliberate ordering of the positions of all of the unbolting places on the coding discs in accordance with the combination permits the lock mechanism to be actuated by "inner" unbolting for opening purposes. The ordering of the coding discs for opening remains set. After the door has been relocked this setting is not automatically canceled. The cancellation of the ordering must be performed very deliberately and is known as code scrambling. The scrambling of the code must not be forgotten, although unfortunately this often happens in practice such that the ordered coding discs permit a door firmly locked by the bolts to be reopened.
The proper scrambling of the opening code involves varying the condition of each of the coding discs (usually three to four discs can be used). Casual scrambling may turn the release groove of a single disc through only ten degrees of angle permitting a properly locked and bolted door to be unbolted again and opened by a skillful exploitation of this circumstance, i.e., by a slight turn of the combination knob.
Persons entitled to perform opening and closing of the door generally do not understand the function of the lock, and must adhere strictly to the operating instructions to avoid errors. One step which is of concern is the periodic changing of the opening code. In spite of thorough training, errors are repeatedly made in this procedure. The most unpleasant one is that a new code thought to have been inputted, no longer unbolts the lock such that the door can no longer be opened. The fear that this may occur results in the original code, set at the factory, being retained for years on end, even through personnel fluctuate and the code may have become known to unauthorized persons.
In practice, a locking system has a hard safety aspect and a soft safety aspect which must be given equal importance. It is unimportant whether a burglary is the result of errors amounting to negligence, or harder measures including safe cracking.